Ash-free coal production method

ABSTRACT

Provided is a method that controls and uniformizes fluidity of ash-free coal. The method includes the steps of obtaining an ash-free coal by removing a solvent from a solution containing a coal component dissolved therein (ash-free coal obtaining step (solvent recovering unit  8 )); and mixing a plurality of coals of different types or components thereof, where the coals are capable of individually giving ash-free coals having different fluidities (mixing step (see reference signs B 1  to B 6 )). The ash-free coal obtaining step (solvent recovering unit  8 ) obtains the ash-free coal by removing the solvent from the solution containing components of the coals which have been mixed.

TECHNICAL FIELD

The present invention relates to a method for producing an ash-freecoal.

BACKGROUND ART

There have been ash-free coals obtained by removing ash from coals.Patent Literature (PTL) 1 discloses a customary method for producing anash-free coal. The ash-free coal production method produces the ash-freecoal by mixing coal with a solvent; removing solvent-insoluble ash froma coal component dissolved in the solvent (soluble coal component) toleave a solution containing the soluble coal component in the solvent;and removing the solvent firm the soluble coal component (from thesolution).

PTL 1 describes a technique for improving the settling velocity of asolvent-insoluble component by blending general coal with caking coal(e.g., claim 1 and paragraph [0008] in PTL 1).

Suitable fluidity (thermoplasticity) of an ash-free coal variesdepending on the intended use thereof. The use is exemplified by coalfor coke making and a fuel typically for a boiler. Fluidity control isimportant particularly when the ash-free coal is used as coal for cokemaking.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication (JP-A) No.2009-227718

SUMMARY OF INVENTION Technical Problem

A possible solution to control the fluidity is blending of pluraldifferent ash-free coals having different fluidities from each other.However, if plural different ash-free coals are blended (i.e., ifash-free coals produced individually are blended) to give an ash-freecoal, the resulting ash-free coal suffers flora uneven distribution offluidity, i.e., it includes portions with high fluidity and portionswith low fluidity. The ash-free coal having such unevenly distributedfluidity, particularly when used as coal for coke making, causes thecoke to suffer from unevenly distributed strength.

Accordingly, an object of the present invention is to provide anash-free coal production method that can control and uniformize thefluidity of the ash-free coal.

Solution to Problem

The present invention provides an ash-free coal production method thatincludes the steps of preparing a slurry by mixing coal with a solvent(slurry preparation step); extracting a component of the coal soluble inthe solvent (solvent-soluble coal component) to give an extractionproduct by heating the slurry prepared in the slurry preparation step(extraction step); separating a solution from the extraction productextracted in the extraction step, the solution containing thesolvent-soluble coal component (separation step); and obtaining anash-free coal by removing the solvent from the solution separated in theseparation step (ash-free coal obtaining step). The ash-free coalproduction method further includes the step of mixing a plurality ofcoals of different types or components thereof at a timing before theash-free coal obtaining step, where the coals are capable ofindividually giving ash-free coals having different fluidities from eachother. The ash-free coal obtaining step obtains the ash-free coal byremoving the solvent from a solution containing components of the coalswhich have been mixed.

Advantageous Effects of Invention

The present invention can control and uniformize the fluidity of anash-free coal.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of ash-free coal production equipment tocarry out the ash-free coal production method.

FIG. 2 is a graph illustrating how the fluidity of an ash-free coalvaries depending on the temperature.

DESCRIPTION OF EMBODIMENTS

With reference to FIG. 1, the ash-free coal production equipment 1 tocarry out the ash-free coal production method, and the ash-free coalproduction method will be sequentially illustrated.

The ash-free coal production equipment 1 is an apparatus to produce anash-free coal by removing ash from a material coal (hereinafter alsosimply referred to as “coal”). The “ash” refers to a substance thatremains after something is burnt. The ash-free coal production equipment1 includes a slurry preparation tank 2 that mixes a coal and a solventwith each other to prepare a slurry a preheater 3 connected to theslurry preparation tank 2; an extractor 4 connected via the preheater 3to the slurry preparation tank 2; a solution separating unit 5 connectedto the extractor 4; a solvent recovering unit 6 and a filter 7respectively connected to the solution separating unit 5; and a solventrecovering unit 8 connected via the filter 7 to the solution separatingunit 5. The ash-free coal production equipment 1 also includes a solventcircuit 9 that connects the solvent recovering unit 8 and the sol ventrecovering unit 6 to the slimy preparation tank 2.

The ash-free coal production method is carried out with the ash-freecoal production equipment 1 and produces an ash-free coal (hypercoal) byremoving ash from a coal. The ash-free coal is a coal containingsubstantially no moisture and little ash. The ash-free coal contains ashin a content of typically 5 percent by weight or less, and preferably 3percent by weight or less. The ash-free coal has a higher heating value(heat output), better ignitability, and better burnout quality thanthose of the material coal and is usable as a high-efficient fueltypically for boilers. The ash-free coal has higher fluidity(thermoplasticity) than that of the material coal and is usable as amaterial or part of material (opal blend) for coke for iron making use.The ash-free coal production method includes a slurry preparation step,a preheating step, an extraction step, a separation step, a filtrationstep, an ash-free coal obtaining step, and a recycling step in thisorder. The ash-free coal production method further includes a mixingstep and a mixing ratio determining step upstream tom the ash-free coalobtaining step. The ash-free coal production method may further includea residue coal obtaining step downstream from the separation step.

The slurry preparation step is performed in the slurry preparation tank2 and is the step of mixing coal with a solvent to prepare a slurry.Details of the slurry preparation step are as follows. A coal is fedfrom a feeder (not shown) to the slurry preparation tank 2. A solvent isfed from a solvent circuit 9 to the slurry preparation tank 2. Theslurry preparation tank 2 mixes the fed coal and solvent with each otherto prepare a slurry. The concentration of the coal relative to thesolvent is preferably from 10 to 50 percent by weight, and morepreferably from 15 to 35 percent by weight on a thy coal basis. Theprepared slurry is fed from the slurry preparation tank 2 via thepreheater 3 to the extractor 4.

The solvent used in the slurry preparation step is one capable ofdissolving the coal therein. The solvent is preferably one having a highpercentage (extraction rate) of a soluble coal component to beextracted. The solvent is exemplified by a solvent containing anaromatic compound and will be described in detail later. Specifically,the solvent is exemplified by methylnaphthalene oil and naphthalene oil,which are distillate oils of byproduct oils obtained when coal issubjected to carbonization to produce coke. The solvent preferably hassuch a boiling point as to provide a high extraction rate in theextraction step and a high solvent recovery rate in the ash-free coalobtaining step and has a boiling point of typically preferably front180° C. to 300° C., and more preferably from 230° C. to 280° C.

The solvent will be illustrated in further detail below. The solvent mayfor example be an aromatic solvent. Such aromatic solvents include anon-hydrogen-donor solvent and a hydrogen-donor solvent.

The non-hydrogen-donor solvent is a solvent that is a coal derivativeand is purified mainly from carbonization products of coal. Thenon-hydrogen-donor solvent contains, as principal components, bicyclicaromatic compounds. The bicyclic aromatic compounds are exemplified bynaphthalene, methylnaphthalene, dimethylnaphthalene, andtrimethylaphthalene. The non-hydrogen-donor solvent further containsother components such as naphthalenes, anthracenes, and fluorenes, eachof which has an aliphatic side chain; and alkylbenzenes corresponding tothem, except being added with biphenyl and/or a long-chain aliphaticside chain. The non-hydrogen-donor solvent is stable even under heating,has high dissolving power with respect to the coal (has excellentaffinity for the coal), and exhibits a high extraction rate of the coalcomponent. The non-hydrogen-donor solvent can be easily recovered by aprocess such as distillation.

A hydrogen-donor compound (including a coal-derived liquid) constitutingthe hydrogen-donor solvent is exemplified by1,2,3,4-tetrahydonaphthalene. The hydrogen-donor solvent, when used asthe solvent in the slurry preparation step, provides a higher yield ofash-free coal than that of the non-hydrogen-donor solvent.

The preheating step is a step that is performed in the preheater 3 andpreheats the slurry to be introduced to the extractor 4. It isacceptable that the method does not include the preheating step.

The extraction step is a step that is performed in the extractor 4 andheats the slurry prepaid in the slurry preparation step (slurrypreparation tank 2) to extract a coal component soluble in the solvent(hereinafter also referred to as a “solvent-soluble component”). Organiccomponents in the coal are extracted in the extraction step. Details ofthe extraction step are as follows. The slurry fed to the extractor 4 isheated to and held at a predetermined temperature while being stirredwith a stirrer arranged in the extractor 4. This process extracts thesolvent-soluble component from the slurry. However, the extractionproduct contains not only the solvent-soluble component, but also ashand other components that are insoluble in the solvent (hereinafter alsoreferred to as “solvent-insoluble components”). The extraction productis fed from the extractor 4 to the solution separating unit 5.

The slurry heating a in the extraction step is performed at such atemperature as to allow the solvent-soluble component to be dissolved inthe solvent. Specifically, the slurry heating may be performed at atemperature of typically preferably from 300° C. to 420° C., and morepreferably from 350° C. to 400° C.

The slurry heating (extraction) in the extraction step is prefer-ablyperformed for such a time as to allow the solvent-soluble component tobe dissolved in the solvent sufficiently and as to extract thesolvent-soluble component at a sufficiently high extraction rate.Specifically, the heating may be performed for a time of preferably from5 to 60 minutes, and more prefer-ably from 20 to 40 minutes. When theslurry is heated (preheated) in the preheater 3, the “heating time”refers to a total heating time in the preheater 3 and in the extractor4.

The extraction step is preferably performed in the presence of an inertgas. Of such inert gases nitrogen gas is typically preferred because ofits inexpensiveness. A pressure to be applied to the slurry in theextraction step is preferably from 1.0 to 20 MPa, although it may varydepending on the temperature and the vapor pressure of the solvent to beused in the extraction.

The separation step is a step that is performed in the solutionseparating unit 5 and separates a solution from the extraction productextracted in the extraction step, which solution contains thesolvent-soluble coal component. Details of the separation step are asfollows. The solution separating unit 5 separates the fed extractionproduct into a solution and a solids-enriched fluid. The solution is, asolution containing the solvent and, dissolved therein, thesolvent-soluble component. The solids-enriched fluid is a slurry fluid(slurry) containing ash, and other solvent-insoluble components. Thesolids-enriched fluid is fed from the solution separating unit 5 to thesolvent recovering unit 6. The solution is fed from the solutionseparating unit 5 via the filter 7 to the solvent recovering unit 8. Thesolution separating unit 5 is exemplified by a gravitational settlingtank that separates the solution typically by gravitational settling; afiltering device that separates the solution typically by filtration;and a centrifugal separator that separates the solution typically bycentrifugal separation.

The residue coal obtaining step is a step that is performed in thesolvent recovering unit 6 and evaporates and removes the solvent fromthe solids-enriched fluid to thereby yield a residue coal. The residuecoal is a coal including ash and other solvent-insoluble componentsconcentrated therein. The residue coal is usable typically as part of acoal blend for coke making. Details of the residue coal obtaining stepare as follows. The solvent recovering unit 6 removes or separates thesolvent from the fed solids-enriched fluid by evaporative separation torecover the solvent. The evaporative separation will be described later.The solvent recovering unit 6 thus removes the solvent from thesolids-enriched fluid and yields a residue coal. The recovered solventis fed (recycled) from the solvent recovering unit 6 via the solventcircuit 9 to the slurry preparation tank 2. It is acceptable that themethod does not include the residue coal obtaining step.

The filtration step is a step that is performed in the filter 7 andfiltrates of a solid contaminated in the solution separated in theseparation step. It is acceptable that the method does not include thefiltration step.

The ash-free coal obtaining step is a step that is performed in thesolvent recovering unit 8 and removes the solvent from the solutionseparated in the separation step to give an ash-free coal. Details ofthe ash-free coal obtaining step are as follows. The solvent recoveringunit 8 removes (separates) the solvent from the fed solution byevaporative separation. The evaporative separation may be performed by aseparation process such as a regular distillation process or evaporationprocess (e.g., spray drying). The evaporated and separated solvent isfed (recycled) from the solvent recovering unit 8 via the solventcircuit 9 to the slurry preparation tank 2. Specifically, the solvent iscirculated in the ash-free coal production equipment 1 (solventrecycling step). Thus, the solvent recovering unit 8 removes the solventfrom the solution to give an ash-free coal.

The ash-free coal obtaining step is the step of separating the solventfrom a solution to give an ash-free coal, which solution containscomponents of coals mixed in the mixing step as mentioned below. In thefollowing description, an apparatus or device in which a step isperformed may be indicated as parenthesized.

Mixing Step

The mixing step is the step of mixing a plurality of coals of differenttypes or the step of mixing components of such coals, where the coalsare capable of individually giving ash-free coals having differentfluidities. The fluidities will be described later. The mixing step isperformed at a timing before the ash-free coal obtaining step and mixescoals or components thereof. The term “a timing before the ash-free coalobtaining step” refers to, of steps for obtaining an ash-free coal, astage or step upstream from the ash-free coal obtaining step and doesnot include a step or stage in or after (downstream from) the step ofobtaining a residue coal alone. Embodiments of the timing at whichcomponents of the coals are mixed are as follows.

B1: In an embodiment, the mixing step is performed at a timing beforethe slurry preparation step (the slurry preparation tank 2).Specifically, the material coal A and the material coal B1 are mixedwith each other to give a mixture before being fed to the slurrypreparation tank 2, but the mixture is fed to the slurry preparationtank 2. In another embodiment, the material coal A and the material coalB1 are separately fed to the slurry preparation tank 2 and are mixedwith each other in the slurry preparation tank 2.

B2 and B3: In embodiments, the mixing step is performed at a timingafter the slurry preparation step (the slurry preparation tank 2) andbefore the extraction step (extractor 4). In this case, the term “mixingstep” refers to a “step of mixing coals”.

Specifically, in an embodiment, the mixing may be performed typically bymixing a slurry containing the coal A with the coal B2 (by adding thecoal B2 to the slurry containing the coal A from above).

In another embodiment, the mixing may be performed by mixing a slurrycontaining the coal A with a slurry containing the coal B2. Morespecifically, the mixing may be performed by preparing a slurrycontaining the coal A in a first slurry preparation step; separatelypreparing a slurry containing the coal B2, in a second slurrypreparation step; and mixing the slurries with each other.

In another embodiment, the slurry containing the coal A may be subjectedto the preheating step (preheater 3) and then mixed with the coal B3 (orwith a slurry containing the coal B3).

B4: In an embodiment, the mixing step is performed at a timing after theextraction step (extractor 4) and before the separation step (solutionseparating unit 5). Specifically, the mixing step may be performed bymixing an extraction product containing a component of the coal A withan extraction product containing a component of the coal B4. In thiscase, the term “mixing step” refers to a “step of mixing components ofcoals”. More specifically, the mixing step may be performed byextracting a first extraction product containing a component of thecoal. A through a first slurry preparation step and a first extractionstep; separately extracting a second extraction product containing acomponent of the coal B4 through a second slurry preparation step and asecond extraction step; and mixing the extracts with each other.

B5 and B6: In embodiments, the mixing step is performed at a timingafter the separation step (solution separating unit 5) and before theash-free coal obtaining step (solvent recovering unit 8). Specifically,in an embodiment, a solution containing a component of the coal A ismixed with a solution containing a component of the coal B5. In anotherembodiment, a solution containing a component of the coal A andundergoing a first filtration step (filter 7) may be mixed with asolution containing a component of the coal B6 and undergoing a secondfiltration step.

Mixing Ratio Determining Step

The mixing ratio determining step is the step of determining a mixingratio of coals or components thereof to be mixed in the mixing step.This mixing ratio is hereinafter also simply referred to as “mixingratio”. The mixing ratio determining step is performed before theindividual steps (a series of production steps performed continuously).Namely, the mixing ratio is prepared in advance. The mixing ratiodetermining step is the step of determining the mixing ratio based ondata D relating to fluidities of ash-free coals individually derivedfrom the coals or components thereof. The data D is hereinafter alsosimply referred to as “data D.”. The data D act as an index offluidities of ash-free coals actually obtained respectively from coalsand are exemplified by maximum fluidity MF mentioned later. The data Dmay also be an index that relates to the fluidities of ash-free coalsindividually derived from the coals and is available without actuallyconverting the coals into ash-free coals respectively. The data D mayfor example be average molecular weights of coals as described in amodification mentioned later.

Next, an embodiment will be illustrated in which ash-free coals areactually obtained from coals, and, based on which, data D relating tofluidity are obtained. The mixing ratio determining step includes anindividual ash-free coal obtaining substep of obtaining ash-free coalsindividually from coals; and a fluidity measuring substep of measuringthe fluidities of the ash-free coals obtained from the individualash-free coal obtaining substep.

The individual ash-free coal obtaining substep is a substep of obtainingash-free coals individually from the coals. Specifically, a firstash-free coal (defined as an “ash-free coal α”) is obtained from asingle (single kind) first coal (defined as the coal A). Separately, asecond ash-free coal (defined as an “ash-free coal β”) is obtained froma single second coal (defined as the coal B). The individual ash-freecoal obtaining substep may be performed with an apparatus similar to oridentical to the ash-free coal production equipment 1. The individualash-free coal obtaining substep may also be performed with an apparatusthat can be operate under similar conditions to those of the ash-freecoal production equipment 1, but has a simpler structure as a scaledownof the ash free coal production equipment 1.

The fluidity measuring substep measures fluidities respectively of theash-free coals α and β obtained from the individual ash-free coalobtaining substep. The fluidity measurement is performed by the methodusing a Gieseler plastometer as prescribed in Japanese IndustrialStandard (JIS) M 8801. Specifically, fluidity measuring substepdetermines how the fluidity varies depending on the temperature on eachof the ash-free coals α and β. Exemplary determination results areindicated in FIG. 2 and Table 1 below. The fluidity is expressed in unitof ddpm (dial division per minute) and indicates thermoplasticity of asample. The fluidity measurement typically gives a maximum fluidity MF.The maximum fluidity MF, when exceeding the determination limit, may beestimated from the initial softening temperature and the solidificationtemperature. The terms “initial softening temperature”, “solidificationtemperature”, “fluidity”, and “maximum fluidity” are as defined in JIS M8801.

In the embodiment, the mixing ratio determining step determines themixing ratio of components of the coals A and B based on the fluidities(e.g., maximum fluidities MFs of the ash-free coals α and β,respectively) determined in the fluidity measuring substep. The mixingratio determining step determines the mixing ratio so as to give anash-free coal (ash-free coal γ) having a target fluidity, which ash-freecoal γ is produced by mixing components of the coals A and B with eachother. Typically, the step determines the mixing ratio so as to give anash-free coal γ having a predetermined fluidity between the fluidity ofthe ash-free coal α and that of the ash-free coal β.

Conditions for Plural Different Coals to be Mixed

Next, conditions for the coals to be mixed in the mixing step will bedescribed. The coals are selected so as to give a sufficient differencein fluidity between the ash fine coal α or β and the ash-free coal γ.The ash-free coals α and β have only to be ash-free coals that can beobtained from the coals A and B as a Ingle coal respectively, and thereis no need of actually obtaining them (except in “Effect 2” as mentionedlater).

Details of the conditions for the roads are as follows. The ash-freecoals α and β obtained from the coals A and B, respectively, differ fromeach other in data D on fluidity (e.g., maximum fluidity MF). In apreferred embodiment, the ash-free coals α and β respectively obtainedfrom the coals A and B have a difference (absolute value of thedifference) in maximum fluidity Log MF of 1.0 (Log (ddpm)) or more. Theterm “maximum fluidity Log MF” refers to the logarithm of the maximumfluidity MF. The logarithm is to the base 10. Typically, the ash-freecoals may have a maximum fluidity Log MF of from 4.0 to 110 (Log(ddpm)); whereas the ash-free coal β may have a maximum fluidity Log MFof from 110 to 20.0 (Log (ddpm)).

Specifically, the coals are exemplified by combinations (1) to (3) asfollows: (1) A combination of low-fluidity Coal-M (inexpensive generalcoal) and high-fluidity Coal-O (expensive coal for coke making). Coal-Oand Coal-M will be illustrated in detail later. (2) A combination oflignite that gives, as a single coal, an ash-free coal having highfluidity and bituminous coal that gives, as a single coal, an ash-freecoal having low fluidity. The bituminous coal has an extraction rate(ash-free coal recovery rate) relatively higher than those of othercoals. The lignite is an inexpensive low-quality coal (3) A combinationof general coals that give, each as a single coal, ash-free coals havingdifferent fluidities from each other. In addition to above combinations,various combinations for coals are possible. Instead of theabove-mentioned material coals, various material coals such assubbituminous coal (inexpensive low-quality coal) can be used.

EXAMPLES

An ash-free coal was produced by mixing Coal-O and Coal-M with eachother. Coal-O is a coal for coke making; whereas Coal-M is a generalcoal fir use typically in power generation or in boilers. Coal-O andCoal-M are both “bituminous coal” and are classified as grade B or C inthe prescription of JIS M 1002. Coal-O by itself is a heavy caking coalexhibiting excellent fluidity. Coal-O, when used as a single materialcoal, gives an ash-free coal exhibiting excellent fluidity. Coal-O has amoisture content of 2.0 percent by weight and an ash content of 9.4percent by weight Coal-M by itself is a non-caking coal exhibitinglittle fluidity and is unusable as a coal for coke making. Coal-M, whenused as a single material coal, gives an ash-free coal exhibitingcertain fluidity, but lower than that of the ash-free coal obtained fromCoal-O as a single material coal. Coal-M has a moisture content of 1.9percent by weight and an ash content of 12.9 percent by weight.

The fluidity was determined on three ash-free coals as follows:

“Coal-O ash-free coal”; ash-free coal produced from Coal-O as a singlematerial coal;

“Coal-M ash-free coal”; ash-free coal produced from Coal-M as a singlematerial coal; and

“Coal-O-added Coal-M ash-free coal”: ash-free coal produced by mixingCoal-M and Coal-O in a mixing ratio of the former to the latter of 90percent by mass to 10 percent by mass.

TABLE 1 Initial Maximum Maximum softening plastic Solidificationfluidity temperature range temperature log MF [° C.] [° C.] [° C.] [log(ddpm)] Coal-O ash- 232 330 to 466 499 11.8 free coal Coal-M ash- 247353 to 434 472 9.5 free coal Coal-O added 237 340 to 448 486 10.1 Coal-Mash- free coal

The fluidity measurement results of the individual ash-free coals areindicated in Table 1. How the fluidity varies depending on thetemperature on the individual ash-free coals is indicated as a graph inFIG. 2. “Coal-O-added Coal-M ash-free coal” exhibited fluidity moreexcellent than that of “Coal-M ash-free coal”. “Coal-O-added Coal-Mash-free coal” had a maximum fluidity MF as an intermediate betweenthose of “Coal-M ash-free coal” and “Coal-O ash-free coal”.

Effects

Next, advantageous effects of the ash-free coal production method willbe illustrated with reference to FIG. 1.

Effect 1

The ash-free coal production method includes the slurry preparation step(slurry preparation tank 2) of mixing coal with a solvent to give aslurry; the extraction step (extractor 4) of heating the slurry preparedin the slurry preparation step to extract a solvent-soluble coalcomponent; the separation step (solution separating unit 5) ofseparating a solution from the extraction product extracted in theextraction step; and the ash-free coal obtaining step (solventrecovering unit 8) of removing the solvent from the solution separatedin the separation step to give an ash-free coal.

The ash-free coal production method further includes the mixing step(see reference signs B1 to B6) of mixing coals or components thereofwith each other, where the coals are capable of individually givingash-free coals having different fluidities from each other. The ash-freecoal obtaining step (solvent recovering unit 8) is the step ofseparating or removing the solvent from the solution containing mixedcomponents of coals and thereby obtaining an ash-free coal.

At the stage of the ash-free coal obtaining step (solvent recoveringunit 8), components of coals are uniformly mixed in a solution (liquid),where the coals are capable of individually giving ash-free coals havingdifferent fluidities from each other. This enables control anduniformization of the fluidity of the resulting ash-free coal.

Details of the Effect are as Follows.

Fluidity Control: The coals or components thereof are mixed in themixing step, where the coals are capable of individually giving ash-freecoals having different fluidities from each other. The mixing ratio ofthe coals or components thereof to be mixed determines the ratio amongorganic components contained in the ash-free coal. The ratio amongorganic components in turn determines the fluidity of the ash-free coal.Accordingly, the ash-free coal fluidity can be controlled according tothe mixing ratio of the coals or components thereof. This can provide anash-free coal having desired fluidity according to the intended use. Thefluidity of the ash-free coal, when controlled, less changes (lessvaries) when other material coals are employed to form the ash-freecoal.

Fluidity Uniformization: Assume that ash-free coals (solids) areproduced from coals, and the produced plural different ash-free coalsare mixed with each other. The mixed ash-free coal often suffers fromuneven distribution of fluidity, namely, often includes portions withhigh fluidity and portions with low fluidity. Such an ash-free coalhaving unevenly distributed fluidity, if used as a coal for coke making,causes the coke to include portions with high strength and portions withlow strength (to have unevenly distributed strength). In contrast, whencomponents of coals are mixed at a process or step upstream from theash-free coal obtaining step, the components of the coals are uniformlymixed in a solution (liquid) at the ash-free coal obtaining step. Thisallows the ash-free coal to have an uniformized fluidity and to lesssuffer from the disadvantages of unevenly distributed fluidity.

Effect 2

In an embodiment, the ash-free coal production method further includesthe mixing ratio determining step of preliminarily determining themixing ratio of the coals or components thereof to be mixed in themixing step. The mixing ratio determining step is the step ofdetermining the mixing ratio based on data on different fluidities,where the different fluidities are of ash-free coals individuallyderived from coals or components thereof.

The mixing ratio determining step determines the mixing ratiopreliminarily (before the respective steps), and this contributes tomore reliable control of the ash-free coal fluidity.

Effect 3

In an embodiment, the mixing ratio determining step includes theindividual ash-free coal obtaining substep of obtaining ash-free coalsindividually from the coals; and the fluidity measuring substep ofrespectively measuring fluidities of the ash-free coals obtained fromthe individual ash-free coal obtaining substep. In this embodiment, themixing ratio determining step determines the mixing ratio based on thefluidities determined in the fluidity measuring substep.

The configuration enables further more reliable control of the ash-freecoal fluidity.

Effect 6

In an embodiment, the ash-free coals individually obtained from thecoals have a difference in maximum fluidity Log MF of 1.0 (Log (ddpm))or more.

If the ash-free coals have an excessively small difference in maximumfluidity Log MF, an ash-free coal obtained by mixing coals and anash-free coal obtained without mixing coals have substantially no (orlittle) difference in fluidity from each other. In this case, the mixingof coals becomes meaningless. In contrast, when the ash-free coals havea difference in maximum fluidity Log MF satisfying the condition, themixing of the coals reliably gives an ash-free coal having fluiditydifferent from that of an ash-free coal obtained without mixing coals.

Modification

The mixing ratio determining step is the step of determining the mixingratio based on data D relating to the fluidities of ash-free coalsindividually derived from coals, as described above. The data D may alsobe data obtained without actually converting the coals into ash-freecoals, as described above. Specifically, in an embodiment(modification), the data D may also be average molecular weights M ofcoals A and B, respectively. This will be further described below.

In the modification, the mixing ratio determining step includes thesubstep of measuring average molecular weights M of coals A and B,respectively (molecular weight measuring substep). In the modification,the mixing ratio determining step determines the mixing ratio of thecoals A and B based on the average molecular weights M measured in themolecular weight measuring substep.

Specifically, there is correlation between the average molecular weightM of a single material coal and the fluidity of an ash-free coalobtained from the single coal. More specifically, the plastic range andthe maximum fluidity MF increase with a decreasing average molecularweight (with an increasing proportion of low-molecular-weightcomponents). The term “plastic range” refers to the difference betweenthe initial softening temperature and the solidification temperature. Incontrast, the plastic range and the maximum fluidity MF decrease with anincreasing average molecular weight (with an increasing proportion ofhigh-molecular weight components).

Conditions for Plural Different Coals to be Mixed

Conditions for the coals to be mixed in the mixing step are as follows.The coals A and B have average molecular weights M differing from eachother. The coals A and B preferably have a difference (absolute value ofdifference) in average molecular weight of 30 or more.

The difference in average molecular weight M may be set so as to satisfythe condition in maximum fluidity Log MF as described above. The coalsmay satisfy the condition for the difference in maximum fluidity Log MFas a result of satisfying the condition for the difference in averagemolecular weight M, the coals may satisfy only one of the condition forthe difference in maximum fluidity Log MF and the condition for thedifference in average molecular weight.

Effect 4

Next, the effect of ash-free coal production method according to themodification will be described. In the modification, the mixing ratiodetermining step includes the molecular weight measuring substep ofrespectively measuring average molecular weights of coals. The mixingratio determining step in the modification determines the mixing ratiobased on the average molecular weights measured in the molecular weightmeasuring substep.

Accordingly, the data Don fluidities of ash-free coals individuallyderived from the coats can be obtained without actually producingash-free coals individually from the coals (without undergoing theindividual ash-free coal obtaining substep).

Effect 5

In an embodiment, the coals have a difference in average molecularweight M of 30 or more.

If the coals have an excessively small difference in average molecularweight, an ash-free coal obtained by mixing components of the coals andan ash-free coal obtained without mixing components of the coals havesubstantially no (or little) difference in fluidity from each other. Inthis case, the mixing of components of coals becomes meaningless. Incontrast, when the ash-free coals have a difference in average molecularweight M satisfying the condition, the mixing of (components of) thecoals reliably gives an ash-free coal having fluidity different fromthat of an ash-free coal obtained without mixing coals.

Other Modifications

The mixing ratio determining step determines the mixing ratio based onthe data D on fluidities of ash-free coals individually derived fromcoals, as is described above. In the embodiment and modification asdescribed above, the maximum fluidity MF and average molecular weight Mare respectively employed as the data D. The data D, however, may alsobe other data, as long as having relationship with fluidities ofash-free coals individually derived from the coals. Specifically, thedata D may also be data typically of fluidity at a certain temperature,solidification temperature, initial softening temperature, or plasticrange. The data D may also be a value calculated from a combination oftwo or more data such as maximum fluidity MF, average molecular weightM, fluidity at a certain temperature, solidification temperature,initial softening temperature, and plastic range.

The embodiments take the ash-free coal produced by mixing two differentcoals as an example. The ash-free coal, however, may also be produced bymixing three or more different opals. In this case, the three or moredifferent coals may have a difference in maximum fluidity log MF and/ora difference in average molecular weight so that the difference between,of the three or more coals, one having a maximum value and one having aminimum value satisfies the condition.

REFERENCE SIGNS LIST

1 ash-free coal production equipment

2 slurry preparation tank

4 extractor

5 solution separating unit

7 solvent recovering unit

The invention claimed is:
 1. A method for producing an ash-free coal,the method comprising the steps of: preparing a slurry by mixing coalwith a solvent; extracting a component of the coal soluble in thesolvent to give an extraction product by heating the slurry prepared inthe slurry preparation step; separating a solution containing thesolvent-soluble coal component from the extraction product extracted inthe extraction step; obtaining an ash-free coal by removing the solventfrom the solution separated in the separation step, wherein: the methodfurther comprises the step of: determining a mixing ratio of the coalsor components thereof to be mixed, wherein the mixing ratio determiningstep determines the mixing ratio based on data relating to differentfluidities of ash-free coals individually derived from the coals orcomponents thereof; and mixing a plurality of coals of different typesor components thereof based on the mixing ratio and at a timing beforethe ash-free coal obtaining step, the coals capable of individuallygiving ash-free coals having different fluidities from each other; andthe ash-free coal obtaining step obtains the ash-free coal by removingthe solvent from a solution containing components of the coals whichhave been mixed.
 2. The ash-free coal production method according toclaim 1, wherein: the mixing ratio determining step comprises thesubsteps of: obtaining ash-free coals individually from the coals; andmeasuring fluidities of the ash-free coals respectively obtained fromthe individual ash-free coal obtaining substep; and the mixing ratiodetermining step determines the mixing ratio based on the fluiditiesdetermined in the fluidity measuring substep.
 3. The ash-free coalproduction method according to claim 1, wherein: the mixing ratiodetermining step comprises the substep of measuring average molecularweights of the coals respectively; and the mixing ratio determining stepdetermines the mixing ratio based on the average molecular weightsmeasured in the molecular weight measuring substep.
 4. The ash-free coalproduction method according to claim 3, wherein the coals have adifference in average molecular weight of 30 or more.
 5. The ash-freecoal production method according to claim 1, wherein the ash-free coalsobtained individually from the coals have a difference in maximumfluidity of 1.0 (Log(ddpm)) or more.